The present invention generally relates to flow control devices and, more specifically, to liquid flow control devices for applications in which it is desired to reduce liquid flow at a disproportionate rate at higher pressures. While the preferred embodiment is described with regard to flow control between a reservoir and a livewell mounted on a boat, those of ordinary skill in the art will understand that the present invention has a much wider application, as further discussed below.
The terms "livewell" and "baitwell" are used in this disclosure interchangeably to describe either saltwater or freshwater boat-mounted holding tanks. The term "fresh water" as used below means water brought into the holding tank from outside the boat, whether saltwater or freshwater.
It is widely recognized that successful saltwater fishing with natural bait requires that the bait be kept alive and healthy. Since bait can be quite expensive and fragile, many fishing boats are equipped with means to maintain a continuous circulation of fresh water through the baitwell at all times, whether the boat is moving or not. In freshwater tournament fishing, such as bass and walleye events, the catch is kept in livewells. It is critical in these events to keep the catch alive or the fisherman will be penalized at weigh-in for any dead fish. Tournament catch are released after weigh-in.
A popular type of fishing boat livewell system is shown in FIG. 1. An inlet strainer or high-speed pickup 10 is mounted on boat hull 12, below waterline. The scoop may include a strainer to prevent the intake of waterborne solids. The scoop is connected to a seacock or shut-off valve 13. The outlet of the seacock is connected to the inlet side of pump 15. The pump outlet feeds water to livewell 17. Livewell 17 includes an overflow pipe 19.
When the boat is sitting still in the water or moving slowly, the pump is turned on to provide circulation. Water is drawn in through the inlet strainer and pumped to the livewell. Excess water is drained out overflow pipe 19, maintaining the livewell at a preset level and providing a continuous circulation of fresh water.
When the boat is underway, the pump is turned off and water flow is provided by the inlet strainer. As the boat speed increases, the water pressure acting at the inlet strainer increases due to the relative velocity between the boat and water. A substantial flow of fresh water can be provided in this manner. However, at high boat speeds, the resultant high dynamic pressure at the inlet strainer can produce excessively high pressure at the pump inlet and excessively high flow rate into the livewell. Both high pressure and high flow can cause problems, as now discussed.
Short pump service life is very common in this application. When high pressure acts on the inlet side of the pump, it can cause premature pump seal failure because low-cost marine centrifugal pumps have seals that are not designed for high pressure on the inlet side. Also, the high flow rate causes the pump impeller to rotate continuously, increasing seal wear and motor brush wear. As a result, many manufacturers choose to use expensive pumps which can better withstand the high inlet pressures and flows.
The high flow rates can create other problems. Unless the seacock is manually adjusted, the flow can exceed the overflow capacity, resulting in a flooded boat. Seacocks are generally not located in a convenient place to allow easy adjustment of flow. If the plumbing system has a fixed restriction so that no excess flow condition develops, then it is likely that the pump will be unable to provide adequate circulation when the boat is sitting still. Also, a restriction small enough for typical livewell applications, which may be about 1/4 inch in diameter in some cases, can easily clog with waterborne debris. Alternatively, if the overflow is increased in size to meet the flow demand at the highest boat operating speeds, it adds unacceptable cost and bulk to the plumbing system.
Accordingly, it is an object of the present invention to provide a flow control device which automatically adjusts to environments creating a high inlet pressure so that adequate flow may be provided, such as by using an inexpensive pump, during periods of relatively low inlet pressure, e.g., when a boat is sitting still or moving slowly, while also limiting flow and pressure to an acceptable level during periods of high inlet pressure, e.g., such as when a boat is running at its highest speeds.
It is another object of the invention to provide a flow control device which minimizes pump seal pressure, reduces induced impeller rotation speed, lessens motor brush wear and assures that an overflow system capacity is not exceeded.
It is yet another object of the invention to provide a flow control device which can utilize relatively large flow path dimensions at all operating pressures and flow conditions, allowing it to pass some suspended solid matter without frequent maintenance.
It is still another object of the invention to provide a flow control device which does not require moving parts, so as to provide long, trouble-free service life, and which can be manufactured using materials suitable for use in saltwater and freshwater, and for below waterline installation in boats.